Catalyst and catalytic oxidative dehydrogenation of alkylaromatics and paraffins

Abstract

PCT No. PCT/EP95/02483 Sec. 371 Date Mar. 13, 1997 Sec. 102(e) Date Mar. 13, 1997 PCT Filed Jun. 26, 1995 PCT Pub. No. WO96/01796 PCT Pub. Date Jan. 25, 1996Alkenylaromatics are produced by catalytic oxidative dehydrogenation of alkylaromatics employing a redox catalyst which is bismuth oxide, in combination with an additive compound of an alkali metal and/or an alkaline earth metal, on a titanium diooxide carrier. In a first reaction step, an alkylaromatic starting material is oxidatively dehydrogenated with the redox catalyst in the absence of molecular oxygen with attending reduction of the redox catalyst. In a second reaction step, the reduced redox catalyst is reoxidized with an oxygen-containing gas.

We claim: 
     
       1. A process for the catalytic oxidative dehydrogenation of an alkylaromatic to yield the corresponding alkenylaromatic, which process comprises: providing a redox catalyst, which serves as an oxygen carrier, the redox catalyst being prepared by admixing catalytic component bismuth oxide and a titanium oxide carrier in the presence of lanthanum and an additional catalytic component comprising a compound of a number of the group consisting of alkali metals and alkaline earth metals; oxidatively dehydrogenating the alkylaromatic with the redox catalyst to produce a corresponding alkenylaromatic in a first reaction step, the redox catalyst being reduced in this step; and reoxidizing the reduced redox catalyst with an oxygen-containing gas in a second reaction step.   
     
     
       2. A process as claimed in claim 1, wherein the catalyst contains an inorganic binder. 
     
     
       3. A process as claimed in claim 1, wherein the first and the second reaction steps take place alternately in terms of time or at alternate places and the catalyst is contained in a fixed bed reactor. 
     
     
       4. A process as claimed in claim 3, wherein decoupling of the steps is effected by periodically switching the reactor inlet stream between starting material and oxidizing agent. 
     
     
       5. A process as claimed in claim 4, wherein the spatial decoupling of the steps is effected with the use of a circulating fluidized bed, by circulating catalyst particles cyclically between a dehydrogenation reactor and a regeneration reactor. 
     
     
       6. A process as claimed in claim 3, wherein the catalyst is contained in a fixed bed reactor and a flushing phase, in which a flushing gas flows through the fixed bed reactor, is introduced between the steps. 
     
     
       7. A process as claimed in claim 6, wherein the flushing gas used is CO 2 , N 2 , H 2  O or a noble gas. 
     
     
       8. A process as claimed in claim 1, wherein ethylbenzene is dehydrogenated to styrene. 
     
     
       9. A process as claimed in claim 1, wherein the dehydrogenation is carried out at from 200 to 800° C. and at from 100 mbar to 10 bar at a liquid hourly space velocity (LHSV) of from 0.01 to 20 h -1 . 
     
     
       10. A process as defined in claim 1, wherein the redox catalyst comprises from 5 to 50% by weight of bismuth (3) oxide and from 3 to 30% by weight of K 2  O or Cs 2  O, the remainder being titanium oxide and lanthanum, with the proviso that the sum of the percentages by weight is 100. 
     
     
       11. The process of claim 10, wherein the redox catalyst additionally comprises 5 to 30% by weight of lanthanum oxide, with the proviso that the sum of the percentages by weight is 100.